Shruthi XT Problems (Values Flipping, No Sound, etc.)

Hey guys.
i finished building my Shruthi XT…
When i first fired it up all buttons and potentiometers were working perfect, but there was no sound. So i traced the Sound.
I could only make it to Point 1… at Point 2 there is no sound.
So i started reflowing all the solder. Still no sound, then suddenly on the next turn on/off it startet spinning values like wild.
It was not operateable anymore.
Also when i press OSC 2 Shape it reacts sometimes but like if i pressed the Memory button.
Something is really fucked up.
I tried reflashing the Firmware, which worked with Midi OX. Still the same, also reflowing and cleaning solder joints didnt help any.
Maybe some IC went bad but still i dont know why there is no sound.

I built other much more complicated DIY Synths but it seems i have bad luck with the Shruthi XT :frowning:

Any help would be much appreciated.
Thanks
Patrick

After rechecking everything i saw that the LT1054 on the SMR4 Board has a Crack… so i decided to re-order all the IC’s on reichelt and hope for the best.

Maybe the behaviour is because of wrong voltage output or whatever.
I was only able to measure the RED Voltage points with +4.99V on the SMR4 Board. the green ones gave readings of about +0.631V (instead of -4.99V).

Keeping you updated.

Greets

The problem with the -5V rail surely explains all the problems you have with the filter board (no sound/filtering). This is unrelated to the problems you have with switches/pots on the control board, though.

The LT1054 shouldn’t have blown up in the first place. Make sure that:

  • You are using a 7.5V or 9V PSU.
  • All caps surrounding the LT1054 are correctly polarized.
  • The LT1054 has not been inserted backwards.

Otherwise you’ll fry another one!

It said that i could use a 12V PSU on the Case so i did use a 12V one.

I checked all the capacitors and the LT1054 was inserted correctly.

i hope replacing all the IC’s will fix the control board issue… its behaving like this at 0:47
https://www.youtube.com/watch?v=2G_IHa7vdZk (this is not my video, just to show value flipping)

Just that pressing a button doesnt do anything most of the time…
You got any hint with which IC could be responsible ?
Thanks
Patrick

> It said that i could use a 12V PSU on the Case so i did use a 12V one.

But chances are that your 12V PSU, especially if it is unregulated and cheap, is not a 12V PSU at all but a 14V, 15V, or even 19V PSU.

That’s why I now recommend 7.5V to 9V PSUs.

> i hope replacing all the IC’s will fix the control board

This is unlikely to help.

Have you checked all solder joints? Have you checked that the correct ICs are inserted in the right sockets?

You can also try booting the unit several times with the encoder pressed until it shows “shruthi xt (full control)” on boot.

i reflowed all the solder joints… cleaned off all the flux… double and triple checked the IC orientations, resocketed them several times.
The PSU gives 12.3-12.4 Volts.
I also have a 5V PSU, will but this wont work i guess.

What will the XT Full Control Mode do ?

Greets
Patrick

> What will the XT Full Control Mode do ?

The same Shruthi firmware can be used for 3 devices: original shruthi (with 4 knobs), fcd72’s XT (32 knobs), and the “official” XT (knobs and switches).

Booting the synth with the encoder pressed selects one of these 3 devices.

I’m suggesting this because you might have, by mistake, configured the unit for running in the wrong mode.

Also, check the polarity of the resistor networks.

thanks will try this.
It worked on the first five or six try’s until i flipped the device.

Edit: i feel dumb… it was the Mode i guess i have hit the Encoder when flipping it over to measure the Filter board…

Ok now the only thing left is to replace the LT1054… glad that something works out :smiley:

Greets

well changed the LT1054… but its all the same regarding the voltage readings on the filter board… still no sound, still no correct measurements on the green ones (still measure +0.621V instead of -4.99V).

Will order a 9V PSU and see if it fixes my problem, the LT1054 got really damn hot (the new one) hope this one isnt blown like the old one (it has no cracks yet but why does it get so hot with a 12.3V PSU, is this common ?)

Thanks

Could you post a photo of your filter board, especially a zoom on the power supply section side?

hope this one is ok…

Edit: I also replaced the 7905 and 7805 just in Case… same experience…

You got any pixx showing the other (solder) side of the PCB?

Which voltage do you have on each pin of the 7905 after having removed all ICs except the LT1054?

This is the backside of the PCB… i reflowed it several times.

I will measure the 7905 once i got another PSU… i am just driving to the store to get another one.
be right back…

Ok i now got a 7.5V PSU… the LT1054 still gets hot as hell !
I removed all the IC’s except the LT1054.

The 7905 Pins read the following measured to ground:

Pin marked with 0: - 0.6V ands dropping to about -0.3V
Pin marked with I: - 3V and dropping fast to about -2V
Pin marked with +: it seems this pin is ground ?

Greets

Are you sure about the polarity of C1? Maybe you could try replacing it…

eeehrm… well yeah… i could try checking the polarity of… eehm… C1…
checking polarity of C1 … hmm…

  • is supposed to be on the negative side, right ?
    :open_mouth:
    damnit… i overlooked this one… even after rechecking the resistor values and capacitor polarity several times…

Its making noise now :smiley:

thanks bro!
you saved my day/week/month (y)

Greets
Patrick

Great!

Keep in mind that the few minutes during which you ran it with the wrong polarity might have shortened its life. It might be wise to buy a spare…

I always find the markings of those tantalium caps extremely difficult to make out. I prefer to just base myself on the longer lead being positive.